A weir valve is a valve utilizing a resilient diaphragm to traverse a weir and prevent flow of fluid over the weir. The diaphragm may be lifted off the weir, either hydraulically when released, or mechanically to permit flow over the weir.
One reason a weir valve may be desirable is that its working mechanical parts are isolated from fluid flowing through the valve. Hence, weir valves are found in the biotechnological, pharmaceutical, chemical, food processing, beverage, cosmetic, and dairy industries where protection against product contamination and leakage to the valve, workplace or atmosphere are important considerations.
In such industries, it may be desirable to take samples of, or inject components into, chemicals, beverages or other products flowing through pipes. In certain instances, some liquids are subject to be degraded or changed if full flow is not continuous. Such change or degradation may occur if pockets, dead spaces or quiescent areas exist along the flow lines.